Transcriptomic Analysis of NaCl Stress on Monascus Pigment Biosynthesis and Monascus Flavor Fingerprint in Monascus ruber CICC41233

This study investigated the effects of NaCl on growth, Monascus pigment production, and Monascus flavor profile in Monascus ruber CICC41233. The M.ruber CICC41233 was first cultured on a solid malt-peptone-starch medium containing varying NaCl concentrations (0-6% w/v) to evaluate the growth. Subsequently, different NaCl levels (0%, 1%, 3%, 5%) were added to the fermentation culture to assess their effect on Monascus pigment production and volatile flavor compounds. Results showed that low NaCl (1%) significantly promoted mycelial growth, while high NaCl (5%) significantly inhibited fungi growth. Although NaCl was added on 3 day, the yield of Monascus pigments was lower than that of the control group without NaCl, the production of the total pigments was enhanced by 5.91% for 1% NaCl, while 3% and 5% NaCl led to decreases of 53.31% and 91.23%, respectively, after 6 days, compared with the control without NaCl. The addition of NaCl promoted the production of numerous flavor compounds, which increased over fermentation time, particularly at a concentration of 1%. A total of 46 volatile monomers and 14 dimers were identified across all samples. The monomers included 13 aldehydes, 10 ketones, 8 alcohols, 6 esters, 3 acids, 2 pyrazines, 1 phenol, and 3 other compounds. Transcriptomic analysis revealed that salt stress significantly altered expression of genes involved in Glycolysis / Gluconeogenesis, glycerophospholipid metabolism, amino acid metabolism like phenylalanine metabolism, tryptophan metabolism, and arginine, proline metabolism, and energy metabolism. Key pigment biosynthesis genes were upregulated under 1% NaCl. These findings provide insights into the salt-responsive mechanisms of M. ruber and suggest potential strategies for optimizing pigment and flavor production under mild salinity.